sanity: refactor mirrors checks to be more pythonic

sanity: refactor mirrors checks to be more pythonic

- Use clearer variable names
- Use variable unpacking to reference elements by name rather than index
- Sacrifice a small amount of time (iterate over protocols twice per entry
  rather than once) for clarity: use readable generator expressions with any()
  rather than maintaining state.

(From OE-Core rev: 9d31e1e6ce07991fe360e67295311e62a55603af)

Signed-off-by: Christopher Larson <chris_larson@mentor.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>